IGO REVIEWS. 



many twining stems, such as those of the Hop and the Morn- 

 ing Glory, are apt to undergo. It is plain to see, however, 

 that many stems which revolve do not twist at all ; and those 

 that do never could twist on their axis at every revolution 

 without speedy destruction, — indeed usually do not twist until 

 they have ceased revolving. Every one must have noticed that 

 the growing extremity of a Hop, Convolvulus, or other twiner, 

 when unsupported, hangs over or stretches out horizontally to 

 one side. But it is not so well known that this outstretched 

 portion, while at the proper age, is continually sw^eeping 

 round, in circles widening as it grows, and always in the same 

 direction, in search of some object round which to twine. The 

 Hop revolves with the sun ; the Convolvulus, Bean (Phaseo- 

 lus), etc., against the sun, that is, in the same directions that 

 they twine. Two or three internodes are usually revolving at 

 the same time. Mr. Darwin observed thirty-seven revolutions 

 in one internode of a Hop, — the first revolution made in about 

 twenty-four hours, the second in nine hours, the third and the 

 following ones up to the eighth in a little over three hours 

 each. " The shoot had now grown 3^ inches in length, and 

 carried at its extremity a young internode an inch in length, 

 which showed slight changes in its curvature. The next or 

 ninth revolution was effected in two hours and thirty minutes. 

 From this time forward the revolutions w^ere easily observed. 

 The thirty-sixth revolution was performed at the usual rate ; 

 80 was the last or thirty-seventh, but it was not quite com- 

 pleted ; for the internode abruptly became upright, and after 

 moving to the centre became motionless. I tied a weight to 

 its upi^er end, so as slightly to bow it, and thus to detect any 

 movement ; but there was none. Some time before the last 

 revolution the lower part of the internode had ceased to move. 

 ... It moved during five days ; but the more rapid move- 

 ment after the third revolution lasted during three days and 

 twenty hours. The regular revolutions from the 9tli to the 

 36th inclusive, were performed at the average rate of 2 h. 

 31 m. The weather was cold, and this affected the tempera- 

 ture of the room, especially during the night, and consequently 

 retarded a little the rate of movement. . . . After the seven- 



